Method of forming polyethylene gaskets in container closures



Jan. 5, 1965 J. D. NAGLE ETAL METHOD OF FORMING POLYETHYLENEJ GASKETS IN CONTAINER CLOSURES Filed Oct. 5l, 1962 United States Patent 3,164,485 METHOD F FORMKNG PLYETHYLENE GASKETS IN CNTAINER CLSURES .lohn D. Nagle, Belmont, and Charles W. Simons, Bedford, Mass., assignors to W. R. Grace Si Co., Cambridge, Mass., a corporation of Connecticut Filed Oct. 31, 1962, Ser. No. 234,494 3 Claims. (Cl. 117-43) This invention relates to a method of forming sealing gaskets in container closures. In one particular aspect, it relates to a method for forming substantially inert sealing gaskets in metal orplastic caps to be applied to glass jars or bottles.

This application is a continuation-in-part of the copending application Method of Producing Gaskets for Container Closures, Serial No. 193,628, filed May 9, 1922, now Patent number 3,118,783, granted Jan. 21, 19 4. v A

A large proportion of container closures are provided with rubbery gaskets which have been deposited on the closures in the form of a liquid sealing composition and then solidified. While the rubbery gaskets so formed give generally satisfactory sealing performance, they also have certain drawbacks both in the method of their aplication and in the characteristics of the finished gasets.

The gaskets used in caps and similar removable container closures must be quite thick in o rder to provide an adequate seal. Consequently, a heavy'layer of liquid sealing composition must be deposited on the closure and then converted to solid form. The liquid compositions used for the production of ysuch gaskets have been for the most part either water dispersions of suitable elastomers or plastisol compositions. In a few cases, heavy, doughlike mixtures of rubber, filler and a rubber solvent have been used. The water-based compositions require a substantial time for drying, often 60 to 90 minutes. Solventbased compositions ordinarily require an even longer drying time, two hours or more representing a normal drying cycle for gaskets of this type. As a consequence, the use of solvent-based compositionsfor this purpose hasV been Aseverely limited. Plastisol compositions require a relatively short time for uxing or heat-setting, but the range of materials which may be used in such compositions lis very narrow.

Recent developments in the technology of producing and handling elastomeric polymers have made possible the production of solutions and dispersions of the polymers in organic liquid vehicles which, except for the above-described length drying time, would be ideal for use as liquid sealing compositionsto form gaskets for superior sealing ability and excellent adhesion to the container closure. Substitution of these-materials for water-based or plastisol compositions would give greater latitude in the selection of elastomeric polymers and fillers, thus making it possible to use polymers of lower cost or those having special properties such as a high degree of resistance to the action of oils and solvents.

The copending application, Serial No. 193,628,` provides -a method for converting non-aqueous liquid-sealing compositions to gaskets having excellent sealing characteristics in a relatively short periodof time. The gaskets are formed rapidly and economically and have the exact contours and placement desiredV for a given sealing application. Briefly stated, the methoddisclosed in the p'ersed in an organic solution of a substantially inert 3,164,485 Patented Jan. 5, 1,965

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herent, solid gasket of the desired shape. The liquid sealing composition may lbe a solution or a dispersion of an elastomer in a suitable organic liquid vehicle. It may alsorbe a dispersion of an elastomer in an organic solution of a second elastomer such as that described in U.S. 2,593,681.

One of the main requirements for a gasket for crowns is that it be substantially inert, that is, it must not add to or detract from the natural flavor and odor properties of the contents of the bottle. While the compositions disclosed in the copending application, Serial No. 193,628, provide excellent gaskets, it has now been discovered that Ia highly inert gasket can be rapidly and economically produced by using a non-aqueous liquid sealing composition comprised of finely divided solid polyethylene discompatible polymer.

One embodiment of the present invention is shown in the accompanying drawing. FIGURE 1 is a diagrammatic View illustrating the successive steps of forming -an annular gasket in a crown cap. FIGURE 2 is a crossu sectional view taken on line 2--2 of FIGURE 1 showapplication comprises depositingan annulus'of a nonaqueous liquid sealing composition in aclosure, expelling the liquid from the composition at a rate which forms a i residue to collapse the cells and form a substantially coing the porous dried sealing composition on an enlarged scale. FIGURE 3 is a cross-sectional view taken on line 3-3 of FIGURE l showing the finished gasket afterV compression of the porous composition.

While the invention is described withrespect to the formation of an annular gasket, it is to be understood that the gasket may ber of any desired configuration. nFor example, it may be an over-all lining of :the crown. :i

According to the present invention, the method comprises depositing in the cap 4 an annulus of 4a liquid sealing composition 5 composed of finely divided solid polyethylene dispersed in an organic solution of a substantially inert compatible polymer, expelling the liquid from the composition at a temperature which soften-s the polyethylene and forms a residue 6 having an open porous surface and containing a number lof interconnected cells 6a, and compressing the residue to collapse the cells and form a substantially coherent solid gasket 7 of form-maintaining shape. i

Preferably, the inert polymer is polyisobutylene or substantially inert copolymers of isobutylene wherein the iso- `butylene is present in` major amount. Unvulcanized butyl rubber made by copolymerizing at least V percent by weight of isobutylene with a dioleiin,` such as isoprene or butadiene, is satisfactory. The molecular weight of the isobutylene polymer is not critical and is dependent largely upon the type of gasket desired. The somewhat tacky solids having molecular Weights from about 80,000t0 100,000 are preferred due to their plasticizingeffect on the polyethylene. The isobutylene copolymer is soluble in solvent-s such as hexane at room temperature whereas polyethylene is not soluble in any solvent at room temperature. It is possible, therefore, to have a much higher polymer content in the sealing composition than would be possible if all the polymers were in solution.

The polyethylene can be prepared by any of the methods which are usually employed for the preparation of these polymers. The polyethylene produced by the high pressure, high temperature polymerization process disclosed in U.S. 2,153,553 to Fawcett et al. is preferred because it is free of catalyst contaminators. .i

The molecular weight of the polyethylene should be at least 600 to provide'tough, durable gaskets. Ethylene Y polymers with-molecular weights below 6000 are toosoft r ent in an amount'equivalent to at least 50 percent ,by

, of its inertness characteristics.

Vthe polyethylene may Ibe present in an amount as high as practicable for a flowed-in sealing composition, Le. 90 percent by Weight of the total polymers present. The polyethylene is non-toxic and inert to almost all materials which are placed in containers having closure caps, eg., it is not attacked by beer, cola drinks or ginger ale.

In addition,'it is an effective binder for the isobutylenev polymer and adheres Wellto the lacquer coating of the closure.

The organic liquid used in the sealing composition is not'criticaland depends largely on the solubility of the inert compatible polymer inthe liquid, as Well as the boiling point, toxicity, availability and cost of the organic liquid itself. Examples of satisfactory liquids are toluene, benzene, pentane, hexane, heptane, octane andthe Various aliphatic alcohols. f

The liquid component of they sealing composition is expelled in a period of minutes or less. During the normal lengthy drying operation of aliquid sealing composition, a continuous skin ordinarily forms over the surface of the composition and prolongs the drying period. In theinstant invention however, the rapid rate of expelling the liquid prevents the formation of the skin. The liquid component of the :sealing composition may be expelled by a number of methods. Preferably, the

A liquid is evaporated at atmospheric pressure by subjecting the composition-containing closure to an elevated ternperature. which produces a puffed porous residue. It should also be high enough to soften the polyethylene.y In general, temy peratures between about 200`F. and 400 F. are satisfactory. At these'temperatures, the gaskets yordinarily used forY sealing glassv jars and bottles require an amount'of sealing composition which will dry in from one to three Y minutes and leave a puffed residue about 0.060 inch thick.

The dry residue in vthe ycontainer closure is a coarse,

The temperature must Vbe Within the range open porous structure containing a large number of interconnected cells and a pervious, open surface through 'which the organic .liquid has been expelled.

vWhile the polyethylene is in a softened state, the residue Viscompressed to an essentially solid, coherent, forrn- Y A satisfactory method is to pass the residue-containing closure l under a die Which simultaneously compresses the residue maintaining gasket by any suitable means;

.by the lip of the Container is no-t sufficient to form the gasket. y Y The compression step makes possible the production of a gasket of the exact contours required for a given f sealing job, a result which is ordinarily diicult to achieve withlloWed-in sealing gaskets. The gasket may, for example, haveV a perfectly flat sealing surface or it may,`if

n desired', be providedwitha lbead at either its inside or out-sideperipheral edge. Thegasketshave such a high degree of dimensional' stability that they are able to main! tain indefinitely the exact configuration imposed` by the sov vtially solid and coherent.

compression step. Placement of the gasket may also be determined during the compression step. As a result of the exact shaping and placement ofthe gasket during the compression step, it is possible to obtain good sealing with an amount of gasketing material substantially less than that ordinarily used.

As an alternative procedure for expelling the liquid ,from the sealing composition, lthecomposition may be held under pressure at a temperature above the boiling point of the liquid until the composition is deposited on the closure, This may be accomplished, for example, by pumping the composition through a'heatV exchanger While holding it under sufficient pressure to maintain it in the liquid state. When the composition is applied to the closure, as by discharge from the nozzle of a lining machine, the sudden release from thepressurized condition forces the liquid to boil oit, or flash off, so quickly that a dry open cellular residue results. The flash drying step will normally be found to form a completely dry residue. Usually the VPolyethylene component of the residue is in a softened state and no additional heating is necessary.

The sealing composition may be modified in various Ways to facilitate the drying and compression steps, to impart the desired properties to the finished gasket and to reduce the cost of the gasket. Forexample, mineral fillers such as zinc oxide, Vcalcium carbonate, barytes, talc,

clay and the like may be added to the composition to aid in preventing formation of a film over the surface of the `composition during drying, thus permitting the quick ex` pulsion of 'the liquid. In addition, fillers also reduce the tackiness of the dried residue thereby preventing it from adhering to the die or other pressure tool which kmay be used in the compression step. Fillers may also be used to give vgreaterbulk and specific sealing characterics to the finished gaskets.' Other minerals such as gums, resins, antioxidants and -thelike may also be addedY to the liquid sealing compositions as desired.

Our invention VWill be more clearly understood by refery ence to the following example, in which all parts are by Weight.

Example 20.0 grams of unvulcanized butyl rubber, al copolymer of isobutylene and isoprene having a maximum Mooney viscosity of'49 at 212 F., (fEnjay YButyl 165) were dissolved lin 100 grams ofhexane at room temperature. v grams of pulverized polyethylene (Petrothene M- 714) were dispersed in the butyl rubber solution. The dispersion was deposited in a series o-f inverted metal caps. The caps were were placed in an oven and subjected to temperatures ranging from` about ZOO-300 F. for about 3 minutes. The residue in leach cap Was highly puffed and porous. The hot residue was compacted under a pressure of about 5() p.s.i. by placing a cold lid of a closure on top of the residue and squeezing them together. The gaskets compacted in this Way Were smooth, substan- They had the appearance of vgaskets dried under conventional conditions for at least 11/2 hours.

We claim: Y

1. A method for preparing a gasketV for a closure element which comprises depositing in the closure element an organic liquid sealing composition composed of 50k to percent by Weight of solid finely-divided polyethylene l dispersed in a volatile organic solution of an isobutylene polymer, said polyethylene having a molecular Weight of at least 6000, evaporating the liquid from the deposited f composition at a temperatureranging from about 200 to y400" F. 'to soften and plasticize the polyethylene and form a residue comprised of a multiplicity of interconsoftened polyethylene and form a substantially solid coherent gasket of a form-stable cor'iiiguratitm;V

The methofijorclaim 1 ijn when the isabutyiene polymer is comprised of at least 95 percent isobutylene copolymerized with up to about 5 percent of a diolein.

3. A method for preparing a gasket for a closure element which compri-ses heating a liquid organic sealing composition to a temperature above the boiling point of its liquid component under superatrnospheric pressure to maintain it in the liquid state, said composition being composed of 50 to 90 percent by weight of solid finelydivided polyethylene dispersed inl a volatile organic solution of an isobutylene polymer, said polyethylene having a molecular Weight of at least 6000, saidheating being suicient to soften and plasticize the polyethylene, depositing the composition in the closure element a't atmospheric pressure to Hash evaporate the liquid to form a residue comprised of a multiplicity of interconnected cells and having an open porous surface, and compressing the residue with means to concurrently cool the softened polyethylene and `form a substantially solid coherent gasket of a form-stable configuration.

5 References Cited in the file of this patent UNITED STATES PATENTS 1,427,133 Taliaferro Aug. 29, 1922 2,114,308 McGowan et al. Apr. 19, 1938 2,238,681 Dorough Apr. 15, 1941 2,336,944 Madge et al. Dec. 14, 1943 2,684,774 Aichele July 27, 1954 2,706,183 Carter Apr. 13, 1955 3,032,826 Brillinger May 8, 1962 3,037,474 Navikas June 5, 1962 FOREIGN PATENTS 615,282 Canada Feb. 28, 1961 OTHER REFERENCES Rolf: Fibers,' Plastics, and Rubbers, 1956, London, Butterworths Scientific Publications, pp. 137-141.

Golding: B Polymers and Resins, New York, Van Nostrand Co., June 1959. 

1. A METHOD FOR PREPARING A GASKET FOR A CLOSURE ELEMENT WHICH COMPRISES DEPOSITING IN THE CLOSURE ELEMENT AN ORGANIC LIQUID SEALING COMPOSITION COMPOSED OF 50 TO 90 PERCENT BY WEIGHT OF SOLID FINELY-DIVIDED POLYETHYLENE DISPERSED IN A VOLATILE ORGANIC SOLUTION OF AN ISOBUTYLENE POLYMER, SAID POLYETHYLENE HAVING A MOLECULAR WEIGHT OF AT LEAST 6000, EVAPORATING THE LIQUID FROM THE DEPOSITED COMPOSITION AT A TEMPERATURE RANGING FROM ABOUT 200 TO 400*F. TO SOFTEN AND PLASTICIZE THE POLYETHYLEN AND FORM A RESIDUE COMPRISED OF MULTIPLICITY OF INTERCONNECTED CELLS AND HAVING AN OPEN POROUS SURFACE, AND COMPRESSING THE RESIDUE WITH MEANS TO CONCURRENTLY COOL THE SOFTENED POLYETHYLENE AND FORM A SUBSTANTIALLY SOLID COHERENT GASKET OF A FORM-STABLE CONFIGURATION. 